Apparatus and method for removing water vapor from a production plant discharge

ABSTRACT

A method and apparatus for removing water vapor from the flue gas stream of an industrial process, including flue gas from a power station. The apparatus including a moisture transfer device, a cooling device, and an optional enthalpy exchange device. The method including running high volumes the flue gas through the moisture transfer device, the cooling device, and the enthalpy exchange device to remove substantially all of the water vapor from the flue gas stream. Also, a method and apparatus for capturing CO 2  from flue gas with very low water vapor content. The apparatus including one or more towers packed with a solid sorbent, or including a liquid sorbent. The CO 2  from the water vapor free CO 2  stream is sorbed by the sorbent and captured for later use.

This nonprovisional application claims the benefit of U.S. ProvisionalApplication No. 61/441,686, filed Feb. 11, 2011.

BACKGROUND

Exhaust stacks of power plants and other fossil fuel burning machinerycontain high levels of both water vapor and CO₂. There is muchdiscussion regarding the removal and capture of CO₂ from these streamsin an effort to abate global warming concerns. However, adsorbent andabsorbent materials, which are attracted to CO₂, also have a strong orpreferential attraction for H₂O, thus their use in CO₂ capture has thusfar not been considered practical.

State of the art systems thus far developed utilize amines(monoethanolamine (MEA), for example) or amino acid salts to absorb theCO₂ in an absorption unit and then transfer the amines to a stripperunit where heat, or heat and a reduction in pressure are used to desorbthe CO₂ into a separate concentrated stream. The concentrated CO₂ streamis then available for use or sequestration.

A primary factor in preventing an increased adoption of this technologyfor sequestration is the energy penalty incurred through the desorptionprocess. NETL report “Cost and Performance Baseline for Fossil EnergyPlants Volume 1: Bituminus Coal and Natural Gas to Electricity” Vol. 1,DOE/NETL-2007/1281, (revised November 2010), details capital andoperating costs for various types of power plants with and withoutcarbon capture, and is summarized in “Fossil Energy Power Plant DeskReference (DOE/NETL-2007/1282). Conclusions of the study show powerplant efficiency is reduced from 6-12 percentage points with theaddition of Carbon Capture and Sequestration (CCS).

The loss in performance is primarily due to the high thermal requirementfor stripping the CO₂ from the amine solution. For example, in thedetailed report noted above, case 13 and 14 of a Natural Gas CombinedCycle (NGCC) plant operates without CCS and produces 555 MW of powerwith a Net plant efficiency of 50.2% (HHV) (see table 5-7). With CCS,the output is reduced to 473 MW (14% reduction in power) and NetEfficiency reduced to 42.8% (HHV) (See Exhibit 5-18). A portion of theloss in output is due to the physical operation of the secondary aminesystem, and the added demand of compressing the CO₂ (totalingapproximately 27 MW of required power to achieve). However, the largerloss is due to the Steam Turbine output reduction as heat is transferredfor amine stripping (or regeneration). In the above examples 188 MW ofthermal energy is transferred from productive use powering the LowPressure Turbine to strip the amine solution, resulting in a loss of 54MW of electrical output.

The required thermal energy for the stripper in this example amounts to3,716 KJ/KG of CO₂ stripped. This is considerably higher than thespecific heat of vaporization of CO₂, which is just 571 KJ/KG.Theoretically CO₂ should be able to be adsorbed and desorbed by asorbent in a similar fashion to water vapor being adsorbed and desorbedby a desiccant. In the case of desiccant regeneration, energy needs havebeen demonstrated to require only 125% of the heat of condensation andcertainly below 200%. It would then follow that the same should be truefor CO₂ with an appropriate sorbent, should water vapor not be presentto detract from the adsorption/desorption process. Therefore, given theH₂O example, it can be concluded that CO₂ should be able to be adsorbedfor a level close to the heat input in the range of 125% to 200% of 571KJ/KG heat of condensation, or between 714 and 1141 KJ/KG.

There is a growing market for the use of CO₂ sources for Enhanced OilRecovery (EOR). Currently it is generally accepted that the market iswilling to pay $20 a ton for the economical use of CO₂ for suchpurposes. However, the high-energy penalties of the current state of theart process cannot support such a low price, without additionalsubsidies. Current discussions pick an achievable cost of not lower than$38/ton CO₂ with the state-of-the-art amine process. The reduction inheat utilization for desorption disclosed herein could play a key rolein helping to reduce production costs of CO₂ through sequestrationcloser to market price for CO₂ as a valued commodity.

SUMMARY

Disclosed herein is a method and apparatus for removing water vapor fromthe stack of a fossil fuel burning facility using substantially only theresidual heat energy in the stack gas stream to perform the work. Havingremoved the water vapor, physical adsorption of CO₂ via numeroussorbents becomes possible, as the CO₂ no longer competes with thefavored water molecule for the attention of the sorption sites.Desorption of the sorbent can now be carried out via a thermal swingprocess where the heat required can approach the heat of vaporizationplus the sorbent's particular heat of sorption plus parasitic losses. Asignificant portion of this heat can be supplied by waste heat sourcesbelow 100 C. The significant reduction in heat required for sorbateregeneration allows more energy to be put to use generating the desiredelectrical output.

In the discussions below adsorption, absorption and sorption are usedinterchangeably, as they are details of the mechanism of attraction of aparticular sorbent. As the most general intent of this disclosure is todetail a cycle for dehydration of a hot gas stream for use in asecondary process, the precise process of sorption may also begeneralized to any of the above terms. The same statement is true forthe use of terms sorbent, adsorbent and adsorbent, which may all be usedinterchangeably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a solid desiccant moisture transferdevice.

FIG. 2 shows an embodiment of a solid desiccant moisture transfer devicehaving a purge system.

FIG. 3 shows an embodiment of a liquid desiccant moisture transferdevice.

FIG. 4 shows an embodiment of a moisture removal system.

FIG. 5 shows an embodiment of a liquid desiccant CO₂ removal system.

FIG. 6 shows an isotherm of EMMIM acetate with varying levels of CO₂.

FIG. 7 shows an isotherm for EMMIM acetate in a 100% CO₂ atmosphere athigher temperatures.

FIG. 8 shows an embodiment of an absorber tower in a CO₂ removal systemoptimized with cooling structures.

FIG. 9 shows an embodiment of a desorber tower in a CO₂ removal systemoptimized with heating structures.

FIG. 10 shows an embodiment of a solid desiccant CO₂ removal system.

DETAILED DESCRIPTION OF EMBODIMENTS

A typical effluent (exhaust) gas stream can have up to about 10% H₂O and10% CO₂ loading. The temperature of the stream varies greatly dependingon the efficiency of the plant and need for wet scrubbers. Inparticular, the newest high-efficiency combined cycle plants have thelowest stack temperature and may require preheating or a reduction inthe output of the secondary turbine, which results in a higher stacktemperature before the method described below may be used. However, manyif not most installed equipment does indeed possess suitable waste heatin the stack stream.

Stack gas (i.e., air and products of combustion after combustion) to bedehumidified may have a minimum temperature of 120° C., such as 130° C.,132° C., 135° C., 140° C., 150° C., 160° C., 163° C. or other valuessignificantly higher. In the case of a non-combined cycle plants thestack temperature may be even higher. If the stack air temperature isbelow this level it may be heated to achieve a higher temperature.

H₂O Vapor Removal

H₂O vapor may be removed from the stack gas before CO₂ capture. Theapparatus for removing H₂O vapor from the stack gas may include thefollowing three components, which are described in more detail below:(1) a moisture transfer device; (2) a cooling device; and (3) anenthalpy exchange device. Additional components may be added as desiredand required without deviating from the scope of this disclosure.

Moisture Transfer Device

The moisture transfer device may include any known means fortransferring moisture from one gas stream to another gas stream. Themoisture transfer device may include, for example, a rotary bed sorptionsystem or a liquid desiccant system.

Referring to FIG. 1, the rotary bed sorption system may include adesiccant wheel 100 that may deliver low dew points, utilizing molecularsieve, silica gel, LiCl or blends of molecular sieves with otherdesiccants or other desiccants. The desiccant wheel 100 may have acorrugated structure that is loaded with desiccant and rotates at lowspeeds. A wet gas stream 110 with low relative humidity enters adesorption portion 120 of the desiccant wheel where moisture istransferred from the desiccant wheel is to the gas stream, thus reducingthe temperature of the gas stream. The desorption portion of thedesiccant wheel that transferred moisture to the gas stream is thusdried. As the desiccant wheel turns, the dried portion of the desiccantwheel is rotated to a different location within the rotary bed sorptionsystem. A second gas stream 130 is then transmitted through anadsorption portion 140 of the desiccant wheel, where the desiccantremoves moisture from the gas stream 130 resulting in a drier gas stream150 exiting the adsorption portion of the desiccant wheel. Thus, a moistdesiccant wheel is generated. The moist desiccant is then moved byrotation of the desiccant wheel to a desorption position where it may beused to add water to gas stream 110.

The rotary bed sorption system may use any suitable desiccant known inthe art. Such desiccants may include silica gel substrates, molecularsieves, and alumina, as well as desiccant salts such as LiBr and LiCl,and CaCl₂ contained within a corrugated or extended surface substrate.

The rotary bed sorption system may use one or more isolation loops toreduce cross-contamination between sorption and desorption zones ofrotary sorption beds caused by pressure imbalances and large vaporpressure differences of the various fluid streams, such as the systemdescribed in U.S. Pat. No. 7,101,414, which is incorporated by referenceherein in its entirety.

A mass of a sorbent material is rotated so that, in a cycle ofoperation, a given volume of the sorbent mass sequentially passesthrough first, second, third, fourth, fifth, and sixth zones, beforereturning to the first zone. A process fluid stream is passed throughthe sorbent mass in the first zone, and a regeneration fluid stream ispassed through the sorbent mass in the fourth zone. A first isolationfluid stream is recycled in a closed loop, independent of the processfluid stream and the regeneration fluid stream, between the sorbent massin the second zone and in the sixth zone. A second isolation fluidstream, meanwhile, is recycled in a closed loop, independent of theprocess fluid stream, the regeneration fluid stream, and the firstisolation fluid stream, between the sorbent mass in the third zone andin the fifth zone.

FIG. 2 illustrates an embodiment of a rotary sorption bed system 200with a closed-loop purge system. The system includes a rotatingdesiccant wheel 210 of a conventional construction containing or coatedwith regenerable sorbent material that, in a cycle of operation,sequentially passes through a first zone 212, a second zone 214, andthird zone 216, and a fourth zone 218. The desiccant wheel 210 isrotated about its axis in the direction indicated by arrow A by a knownrotor mechanism (not shown).

A process fluid stream 220 carrying a sorbate (e.g., water vapor) ispassed through the desiccant wheel 210 in the first zone 212, where thesorbate is sorbed (i.e., loaded) onto the desiccant wheel 210. Theprocess fluid stream exiting the sorbent mass has a reduced sorbateconcentration compared to the process fluid stream entering the sorbentmass.

A regeneration gas stream 240 is passed through the desiccant wheel 210in the third zone 216, in a direction opposite to the flow of theprocess gas stream 220. The sorbate from the process gas stream that wascollected in the desiccant wheel 210 is released into the regenerationgas stream. A heater 250 may optionally be provided to heat theregeneration gas stream 240 prior to its passing through the desiccantwheel 210

An isolation gas stream 270 is recycled in a closed loop, independent ofthe process gas stream 220 and the regeneration gas stream 240, betweenthe desiccant wheel 210 in the second zone 214 and in the fourth zone218. The direction that the isolation gas stream 270 flows through thedesiccant wheel 210 is the same direction as the gas flowing through thezone immediately following the isolation zone in the direction ofrotation of the desiccant wheel 210. In FIG. 2, for example, theisolation gas stream 270 passes through the second zone 214 in the samedirection that regeneration gas stream 240 flows through the third zone216, and passes through the fourth zone 218 in the same direction thatthe process gas stream 220 flows through the first zone 212.Alternatively, the direction that the isolation gas stream flows throughthe sorbent mass could be opposite from the direction of fluid flowthrough the zone immediately following the isolation zone in thedirection of rotation of the sorbent mass. The desiccant wheel mayrotate at speeds of approximately 8-20 rph, such as 10 rph, 15 rph, and17 rph.

In the case of the desiccant rotor, the desiccant structure may beformed into a cylinder rather than a disk so as to be able to processsignificantly larger gas stream than is typically handled by desiccantrotors.

The moisture transfer device may also be a liquid desiccant system.Newly developed ionic liquids with desiccant properties may be used as aliquid desiccant, as these new ionic liquids remain in liquid form evenwith no water loading and, thus, may be suitable for the production ofvery dry gasses.

Referring to FIG. 3, the gas stream to be dehumidified 310 passesthrough a chamber 320. The liquid desiccant is sprayed into the chamberwith the gas stream 310 by a sprayer 330. As the gas stream 310 makescontact with the desiccant it gives up its sorbate, such as water vaporto the liquid desiccant and the gas stream 310 leaves the bed with alower sorbent concentration. The gas stream 310 leaves with a highertemperature as heat of condensation has been released during theadsorption process. The now more dilute sorbent 340, or a portion of themore dilute sorbent, is collected at the bottom of chamber 320 and thentransported to a second chamber 350 where it is brought into contactwith a second, low relative humidity gas stream 360 to remove thesorbate from the liquid desiccant. The liquid desiccant collects in aconcentrated form at the bottom of chamber 350. After which, the liquiddesiccant is returned to the first chamber, or some other adsorptionsite. The system may include recirculation paths limiting the amount ofadsorbent that transfers from the adsorption side to the desorption sidebased on sorbate loading. The chambers may also include dropletseparators 370. A heat exchanger 380 may regulate the temperature of theliquid desiccant as it is pumped from the first chamber to the secondchamber.

The liquid desiccant that may be used in the moisture transfer device isparticularly limited as typical halide salts turn to solid phase whenthe relative humidity drops below low levels and thus are generally notconsidered for use in liquid phase when trying to produce air below 20%relative humidity. Thus, the preferred liquid desiccant may be an ionicliquid; the ionic liquids may have an electric multi-pole moment, suchas an electric dipole moment and/or an electric quadrapole moment. Theionic liquid may be a pure ionic liquid, i.e. a liquid substantiallycontaining only anions and cations, while not containing othercomponents, e.g. water. Alternatively, the initial ionic liquid may be asolution containing the ionic liquid and a solvent or further compound,e.g. water, may be used. In the most generic form, the ionic liquids maybe represented by [Q⁺]_(n)[Z^(n−)], wherein Q represents a cation and Zrepresents an anion, such ionic liquids are disclosed in U.S. patentapplication Ser. No. 13/166,235 that is hereby totally incorporated byreference in its entirety.

Anions of the above ionic liquids may be selected from acetate,fluoride, chloride, thiocyanate, dicyanamide, chlorate, perchlorate,nitrite, nitrate, sulfate, hydrogensulfate, carbonate,hydrogencarbonate, methylcarbonate, phosphate, hydrogenphosphate,dihydrogenphosphate, phosphonate HPO₃ ²⁻, hydrogenphosphonate H₂PO₃ ⁻,sulfamate H₂N—SO₃ ⁻, deprotonated acesulfame, deprotonated saccharine,cyclamate, tetrafluoro-borate, trifluoromethanesulfonate,methanesulfonate, nonadecafluoro-nonansulfonate and p-toluolsulfonate,methylsulfate, ethylsulfate, n-propylsulfate, i-propylsulfate,butylsulfate, pentylsulfate, hexylsulfate, heptylsulfate, octylsulfate,nonylsulfate, decylsulfate, long-chain n-alkylsulfate, benzylsulfate,trichloroacetate, dichloroacetate, chloroacetate, trifluoroacetate,difluoroacetate, fluoroacetate, methoxyacetate, cyanacetate, glykolate,benzoate, pyruvate, malonate, pivalate, the deprotonated or partiallydeprotonated form of the following monovalent or polyvalent acids:formic acid, acetic acid, propionic acid, butyric acid, valeric acid,caproic acid, enanthic acid, caprylic acid, capric acid, lauric acid,myristic acid, palmitic acid, stearic acid, arachidic acid,O-acetylsalicylic acid, sorbic acid, pivalic acid, fatty acids,isoleucine, alanine, leucine, asparagine, lysine, aspartic acid,methionine, cysteine, phenylalanine, glutamic acid, threonine,glutamine, tryptophan, glycine, valine, proline, serine, tyrosine,arginine, histidine, ornithine, taurine, sulfamic acid, aldonic acids,ulosonic acids, uronic acids, aldaric acids, gluconic acid, glucuronicacid, mannonic acid, mannuronic acid, galactonic acid, galacturonicacid, ascorbic acid, glyceric acid, xylonic acid, neuraminic acid,iduronic acid, oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaricacid, glutaconic acid, traumatic acid, muconic acid, citric acid,isocitric acid, aconitic acid, propane-1,2,3-tricarboxylic acid,trimesic acid, glycolic acid, lactic acid, malic acid, citric acid,tartaric acid, mandelic acid, 2-hydroxybutyric acid, 3-hydroxybutyricacid, 4-hydroxybutyric acid, 3-hydroxypropionic acid,3-hydroxyisoyaleric acid, salicylic acid, polycarboxylic acids, PF₆ ⁻,[PF₃(CF₃)₃]⁻, [PF₃(C₂F₅)₃]⁻, [PF₃(C₃F₇)₃]⁻, [PF₃(C₄F₇)₃]⁻,[F₃C—SO₂—N—SO₂—CF₃]⁻, [F₃C—SO₂—N—CO—CF₃]⁻, [F₃C—CO—N—CO—CF₃]⁻,dimethylphosphate, diethylphosphate, dibutylphosphate, dimethylphosphonate, diethyl phosphonate, dibutyl phosphonate, and mixturesthereof.

Cations of the above ionic liquids may be selected fromtetramethylammonium, tetraethylammonium, tetrabutylammoniumtetrahexylammonium, tetraoctylammonium, trimethylammonium,triethylammonium, tributylammonium, triethylmethylammonium,tributylmethylammonium, trihexylmethylammonium, trioctylmethylammonium,tris-(2-Hydroxyethyl)methylammonium, tris-(2-Hydroxyethyl)ethylammonium,bis-(2-hydroxyethyl)dimethylammonium, 1,3-dimethylimidazolium,1-ethyl-3-methylimidazolium, 1-propyl-3-methylimidazolium,1-butyl-3-methylimidazolium, 1,2,3-trimethylimidazolium,1,3-diethylimidazolium, 1,3-dibutylimidazolium,1-ethyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium,1-(2-hydroxyethyl)-3-methylimidazolium,1-(3-hydroxypropyl)-3-methylimidazolium,1-(2-hydroxypropyl)-3-methylimidazolium,1-(4-hydroxy-butyl)-3-methylimidazolium,1-(3-hydroxy-butyl)-3-methylimidazolium,1-(2-hydroxy-butyl)-3-methylimidazolium,1-(2-methoxyethyl)-3-methylimidazolium,1-(3-methoxypropyl)-3-methylimidazolium,1-(2-methoxypropyl)-3-methylimidazolium,1-(4-methoxy-butyl)-3-methylimidazolium,1-(3-methoxy-butyl)-3-methylimidazolium,1-(2-methoxy-butyl)-3-methylimidazolium,1-(2-ethoxyethyl)-3-methylimidazolium,1-(3-ethoxypropyl)-3-methylimidazolium,1-(2-ethoxypropyl)-3-methylimidazolium,1-(4-ethoxy-butyl)-3-methylimidazolium,1-(3-ethoxy-butyl)-3-methylimidazolium,1-(2-ethoxy-butyl)-3-methylimidazolium, 1-allyl-3-methylimidazolium,1-allyl-2,3-dimethylimidazolium, N,N-dimethylmorpholinium,N,N-diethylmorpholinium, N,N-dibutylmorpholinium,N-ethyl-N-methylmorpholinium, N-butyl-N-methylmorpholinium,N,N-dimethylpiperidinium, N,N-diethylpiperidinium,N,N-dibutylpiperidinium, N-ethyl-N-methylpiperidinium,N-butyl-N-methylpiperidinium, N,N-dimethylpyrrolidinium,N,N-diethylpyrrolidinium, N,N-dibutylpyrrolidinium,N-ethyl-N-methylpyrrolidinium, N-butyl-N-methylpyrrolidinium,2-Hydroxyethyltrimethylammonium (choline),2-acetoxyethyl-trimethylammonium (acetylcholine), guanidinium(protonated guanidine, CAS 113-00-8), tetramethylguanidinium,pentamethylguanidinium, hexamethylguanidinium triethylmethylphosphonium,tripropylmethylphosphonium, tributylmethylphosphonium,tetraethylphosphonium, tetrapropylphosphonium, tetrabutylphosphonium,tetramethylphosphonium, and mixtures thereof.

Cooling Device

The cooling device may be any cooling device known in the art, such ascondensers and heat exchangers. In embodiments, the cooling device maybe a finned cooling coil or the like that rejects its heat to preferablyan evaporatively cooled cooling tower. The gas exiting the desorptionside of the moisture transfer device, which is warm and wet, istransferred to the cooling device where it is further cooled and dried.

Enthalpy Exchange Device

The enthalpy exchange device is not particularly limited and may be, forexample, a rotary wheel heat exchanger, a moisture permeable plate heatexchanger, or a liquid desiccant loop where liquid desiccant is passedbetween one air stream and a second air stream. The liquid desiccant maynot require that the two gas streams be passed locally to each other, asthe desiccant exposure surfaces may be connected by piping. Inembodiments, a low flow of liquid desiccant is used to provide themoisture exchange and a heat transfer fluid loop is flowed to providethe heat transfer between the gas streams.

The enthalpy exchange device operates in much the same way as themoisture transfer device. One difference between the moisture transferdevice and the enthalpy exchange device is that the enthalpy exchangedevice is designed and operated in a manner wherein both latent andsensible energy is transferred from one stream to the other, as opposedto the moisture transfer device, which operates so as to maximize latenttransfer while minimizing sensible transfer. It may include an enthalpyexchange material, such as corrugated aluminum coated with a desiccant,or may be a corrugated glassfiber and silicate structure, or others thatare known in the art. The enthalpy exchange device may include at leasttwo portions; an enthalpy-increasing portion and an enthalpy decreasingportion. Warm and/or moist gas enters the enthalpy-decreasing portion ofthe enthalpy exchange device where sensible and or latent energy of thewarm gas is absorbed by the enthalpy transfer material. The enthalpyexchange material that has increased enthalpy due to absorption ofenergy from the warm gas stream is then exposed to cooler gas, where theenthalpy from enthalpy exchange material is transferred to the cool gasstream. The enthalpy exchange material that has been exposed to thecooler gas may then again be exposed to the warm gas stream. Theenthalpy exchange device rotates at a much faster velocity than thedesiccant wheel in the moisture transfer device, such as 10-30 rpm, forexample, 15 rpm, 20 rpm, or 25 rpm. The enthalpy exchange device mayalso have a lower desiccant load and higher specific heat than themoisture transfer device.

The enthalpy exchange device may also be a liquid enthalpy exchangedevice. In such embodiments, the higher enthalpy gas stream may beexposed to an enthalpy exchange medium, where enthalpy from the warm gasstream is transferred to the enthalpy exchange medium, thus increasingthe enthalpy of the enthalpy exchange medium. The enthalpy exchangemedium with increased enthalpy is then exposed to a lower enthalpy gasstream where enthalpy of the enthalpy exchange medium is transferred tothe lower enthalpy gas stream. The enthalpy exchange medium that hasbeen exposed to the lower enthalpy gas stream may then again be exposedto a higher enthalpy gas stream. It is noted that the liquid desiccantand the gas stream need not be physically exposed to one another, thusexposed, as used above, includes any type of exposure that allowsenthalpy exchange.

Reducing Gas Stream Moisture

As stated above, a need exists to reduce the amount of energy that isrequired to capture CO₂. Water has an adsorption energy of about 2326KJ/KG, and CO₂ has an adsorption energy of about 580 KJ/KG. Desiccantdehumidification typically requires 3025 to 4885 KJ/KG of water vaporadsorbed. Thus, a sorbent CO₂ capture system, if all or almost all watervapor is removed, should use about 700 to 1165 KJ/KG, such as 755-1105KJ/KG, 815-1045 KJ/KG, 875-990 KJ/KG, 930 KJ/KG.

Gas stream moisture reduction method may comprise six steps, which aredescribed in more detail below: (1) hot process exhaust gas is passedthrough a desorption portion of a moisture transfer device; (2) thewetted gas is then passed through a cooling device; (3) the cooled gasis then passed through an enthalpy decreasing side of an enthalpyexchange device; (4) the lower enthalpy gas is then passed through anabsorption side of the moisture transfer device; (5) the further driedgas is then delivered to a CO₂ removal system; and (6) the dry and CO₂cleansed gas is passed through an enthalpy increasing side of theenthalpy exchange device. Other various treatments may be performedbefore, between, and after the above steps as desired. The flow of thegas stream is not particularly limited, and may be up to 4,000,000 kg/hrfor a typical power plant. If gas stream entering the system is hotenough, such as 175° C. or above, the enthalpy exchange device andcorresponding process steps may not be required.

Referring to FIG. 4, hot gas or a gas stream heated by a hot gas 410 mayfirst be passed through a desorption portion of a moisture transferdevice 120 to regenerate the desiccant in the moisture transfer device.The values given in FIG. 4 are exemplary values and do not in any waylimit this disclosure. The gas stream may have a temperature greaterthan 95° C., such as 100° C., 105° C., 110° C., 115° C., 120° C., 125°C., 130° C., 135° C. or greater. The relative humidity of the gas streammay be lower than 5%, such as 4%, 3%, 2% or 1%. The absolute humidity ofthe gas stream may be less than 0.1 kg/kg, such as 0.08, 0.06, 0.04,0.03, 0.02 kg/kg or lower. Moisture from the moisture transfer device istransferred from the moisture transfer device to the gas stream. Thus,upon exiting the desorption portion of the moisture transfer device 120,the gas stream 412 will have a lower temperature, higher relativehumidity, and higher absolute humidity.

If the machine and/or plant from which the gas stream is generated isfitted with a wet scrubber, then the gas stream 410 may be used toregenerate the desiccant in the moisture transfer device prior to thewet scrubbing step. If a heated gas stream was used for the regenerationstep, it may either be discarded or combined with a CO₂ laden gasstream.

The cooled and humidified gas stream 412 is then passed through acooling device 420, thus cooling the gas stream to close to the wet bulbtemperature when cooled water from a cooling tower is used as thecooling medium, and significantly reducing its moisture content. Furthermechanical cooling may be employed when wet bulb temperatures do notprovide satisfactory cooling or to provide even drier gas at thedischarge of the process. The cooled and saturated CO₂ laden gas 414leaves with a significant reduction in temperature, but most notably asizeable reduction in moisture content to normal or extreme normalambient levels, such as 6 to 30 g/kg. The temperature of the gas streamexiting the cooling device 414 may be less than 32° C., such as lessthan 30° C., less than 27° C., less than 25° C., less than 20° C., lessthan 17° C., or less than 15° C. The relative humidity of the gas streamexiting the cooling means may be near the saturation level, or 100%.

The further cooled CO₂ laden gas stream may then be passed through anenthalpy-decreasing portion 432 of the enthalpy exchange device 430,significantly reducing the moisture content of the gas stream by aminimum of 50% and preferably more than 70%, such as 75%, or 80%. Thetemperature of the gas will not be significantly affected as theexchange takes place with a lower enthalpy gas stream of similartemperature.

The further dried CO₂ laden gas 416 may next be passed through anadsorption portion 140 of the moisture transfer device in which thedesiccant has been regenerated in the first step by reducing themoisture content of the desiccant to low levels. In embodiments using arotary bed sorption device, as the gas stream here being dried is at atemperature below the dew point of the gas stream being used forregeneration, purge loops may be employed to both help reduce the finaldew point of the gas stream. As discussed above, and disclosed in U.S.Pat. No. 7,101,414, one, two or more purge loops may be required.

This dried air exiting from the absorption portion of the moisturetransfer device 418 may then be delivered to the CO₂ removal system (onesuch system is disclosed separately below) for CO₂ removal.

Finally, the dried and CO₂ cleansed gas 419 may be returned from the CO₂removal system and passed through the enthalpy increasing portion 434 ofthe enthalpy exchange device 430 where the enthalpy exchange deviceremoves sorbent from the CO₂ laden gas prior to the finaldehumidification in the moisture transfer system.

In embodiments where the gas stream is too dirty for direct contact withthe moisture transfer device, such as in a coal fired plant, the stackair is used to heat a separate air stream having a significantly smallervolume than the stack stream, on the order of 20 to 30% of the volume,which is passed through the desiccant means in order to regenerate thedesiccant. The cooled and humidified fresh air is blended with thecooled and treated stack air and may then passed through the aboveapparatus to remove moisture.

CO₂ Removal System

Embodiments of a CO₂ removal system to accompany the above process aredescribed below. The entire process may be used without amino acid saltsor amines as they require water as a solvent to help transport the CO₂.By eliminating the water, which also must go through a phase change, theenergy required to proceed through the phase change of water is. Inembodiments a liquid sorbent is used as it may better concentrate theCO₂ to high levels in a continuous manner. Solid sorbents may also beemployed.

It should also be noted that other di- and multi-pole molecules may alsobe removed in the same manner. Thus it may be possible for thisadsorption system also to remove SOx and NOx compounds in a similarfashion as CO₂, given that the preferential sorbent H2O is no longerpresent. Removal of these compounds in a similar method is herebyincorporated herein.

Liquid Sorbent

In an embodiment using a liquid sorbent, shown in FIG. 5, CO₂ laden gas510 from the moisture removal system described above may enter anabsorber tower 520. It should also be noted that other di- andmulti-pole molecules may also be removed in the same manner. Thus it maybe possible for this adsorption system also to remove SOx and NOxcompounds in a similar fashion as CO2, given that the preferentialsorbent H2O is no longer present. Thus other di- and multi-polemolecules may be interchanged with CO₂ in the following discussion.

A sprayer 522 sprays the liquid sorbent, where it contacts the CO₂ ladengas stream. The sorbent attracts the CO₂ and removes the CO₂ from theCO₂ laden gas stream. The gas from which the CO₂ has been removed isreleased from the absorber tower as a gas 512, where it may be returnedto the moisture removal system as gas stream 419 in FIG. 4. The CO₂,which is bound to the liquid sorbent, is collected at the bottom of theabsorber tower in a liquid state 530. The CO₂ laden liquid may then bepumped to a heat exchanger 540 where it is heated to a temperaturesufficient to vaporize the CO₂ in the liquid sorbent, such as 90° C.,100° C., 110° C., 120° C., or 130° C. The liquid sorbent, which has aCO₂ phase with a reduced vapor pressure, is then pumped to a desorbertower 550. In the desorber tower 550, the CO₂ gas stream 532, which maybe a dry and pure or nearly pure CO₂ stream, is released from thedesorber tower where it may be collected and disposed of or used. As theadsorbent is primarily adsorbing CO₂, the concentration of the CO₂stream can be very pure, namely above 80%, and preferably above 90%. Theliquid sorbent is then collected at the bottom of the desorber tower534, where it has a significantly reduced CO₂ concentration, preferablyless than 50% of the CO2 loading present after the adsorption stage.This regenerated liquid sorbent is then pumped to the absorber towerwhere it may be used as the liquid sorbent 536 that sorbs the CO₂ in theCO₂ laden gas stream from the moisture removal system. A cooler maycondition the liquid sorbent 536 before it is re-introduced into theabsorber tower. The system may also include a cooler 560, a heatexchanger 565, pumps 570, a condenser 575, and a reboiler 580.

Ionic Liquid Sorbent

In this case a liquid sorbent may be an ionic liquid that has a highaffinity for multi-pole molecules, such as dipolar molecules orquadrapole molecules. In embodiments, the ionic liquids may be a pureionic liquid, i.e. a liquid substantially containing only anions andcations, while not containing other components, e.g. water. In the mostgeneric form, the ionic liquids may be represented by [Q⁺]_(n)[Z^(n−)],wherein Q represents a cation and Z represents an anion, which may beproduced by a process as described, for example, in U.S. patentapplication Ser. No. 13/166,235 that is hereby totally incorporated byreference in its entirety.

According to an embodiment, the ionic liquid may have a non-aromaticcation to sorb CO₂, having an electric multipole moment, out of flue gasor gas containing products of combustion. The ionic liquid may be anorganic salt having a melting temperature of below 200° C., of below100° C., and preferably below 20° C. The organic salts may be quaternarysalts having a generic formula of: [Q⁺][RCO₂ ⁻] or [Q⁺][RCO₃ ⁻] or[Q⁺][R^(i)XYC⁻] or [Q⁺][R^(i)R^(j)XC⁻]. The described method can be inparticular useful for all processes in which CO₂ shall be removed fromflue gas. Furthermore, it may be possible to use ionic liquids whichselectively remove CO₂ while do not remove water or water vapor, i.e.hydrophobic ionic liquids may be used.

The anion may be described by one of the following structures:

The anion may be described by the resonant or mesomeric states:

wherein X and Y may indicate, independently from each other, groups thatmay attract electrons due to the inductive effect or the mesomericeffect and/or that may delocalize and/or stabilize (localize) electrons.Examples for such groups may be: —CN, —NO₂, —NO₃, CO—R^(k), —COOR^(k),—C═N—R^(k), —CO—NR^(k)R^(m), —NR^(k)R^(m), —OH, —OR^(k), —SH, —SR^(k),—SO—R^(k), —SO₂—R^(k), —SO₂—OR^(k), —PO—OR^(k)OR^(m) (phosphonate), —I,—Cl, —Br, —F, —CCl₃, —CCl₂R^(k), —CCIR^(k)R^(m), —CF₃, —CF₂R^(k),—CFR^(k)R^(m), —SO₂CF₃, —COOCF₃, C₆H₅, —CR^(k)═CR^(m)R^(n), —C/CR^(m),—CR^(k)═CR^(m)—CN, —CR^(k)═CR^(m)—NO₂, —CR^(k)═CR^(m)—CO—R^(k),—CR^(k)═CR^(m)—COOR^(k), —CR^(k)═CR^(m)—CO—NR^(n)R^(o),—CR^(k)═CR^(m)—NR^(n)R^(o), —CR^(k)═CR^(m)—SR^(n),—CR^(k)═CR^(m)—SO—R^(n), CR^(k)═CR^(m)—SO₂R^(n),—CR^(k)═CR^(m)—S0₂—R^(n), —CR^(k)═CR^(m)—SO₂—OR^(n), —CR^(k)═CR^(m)—CF₃,—CR^(k)═CR^(m)—SO₂CF₃.

R^(k), R^(m), R^(n), R^(o) may, independently from each other, denotehydrogen, C₁- to C₃₀-alkyl and their aryl-, heteroaryl-, cycloalkyl-,halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO—, —CO—O— or—CO—N substituted components, like methyl, ethyl, 1-propyl, 2-propyl,1-butyl, 2-butyl, 2-methyl-1-propyl(isobutyl),2-methyl-2-propyl(tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl,2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl,2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl,3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl,3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl,3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl,3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl,3,3-dimethyl-2-butyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl,nonadecyl, icosyl, henicosyl, docosyl, tricosyl, tetracosyl, pentacosyl,hexacosyl, heptacosyl, octacosyl, nonacosyl, triacontyl, phenylmethyl(benzyl), diphenylmethyl, triphenylmethyl, 2-phenylethyl,3-phenylpropyl, cyclopentylmethyl, 2-cyclopentylethyl,3-cyclopentylpropyl, cyclohexylmethyl, 2-cyclohexylethyl,3-cyclohexylpropyl, methoxy, ethoxy, formyl, acetyl orC_(n)F_(2(n-a)+(1-b))H_(2a+b), wherein n≦30, 0≦a≦n and b=0 or 1 (e.g.CF₃, C₂F₅, CH₂CH₂—C_((n-2))F_(2(n-2)+1), C₆F₁₃, C₈F₁₇, C₁₀F₂₁, C₁₂F₂₅);

C₃ to C₁₂-cycloalkyl and their aryl-, heteroaryl-, cycloalkyl-,halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO— or—CO—O-substituted components e.g. cyclopentyl, 2-methyl-1-cyclopentyl,3-methyl-1-cyclopentyl, cyclohexyl, 2-methyl-1-cyclohexyl,3-methyl-1-cyclohexyl, 4-methyl-1-cyclohexyl orC_(n)F_(2(n-a)−(1-b))H_(2a-b) wherein n≦0, 0≦a≦n and b=0 or 1;

C₂₋ to C₃₀-alkenyl and their aryl-, heteroaryl-, cycloalkyl-, halogen-,hydroxy-, amino-, carboxy-, formyl-, —O—, —CO— or —CO—O-substitutedcomponents (e.g. 2-propenyl, 3-butenyl, cis-2-butenyl, trans-2-butenylor C_(n)F_(2(n-a)−(1-b))H_(2a-b) wherein n≦30, 0≦a≦n and b=0 or 1);

C₃- to C₁₂-cycloalkenyl and their aryl-, heteroaryl-, cycloalkyl-,halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO— or —CO—O—substituted components, (e.g. 3-cyclopentenyl, 2-cyclohexenyl,3-cyclohexenyl, 2,5-cyclohexadienyl or C_(n)F_(2(n-a)−(1-b))H_(2a-b)wherein n≦0, 0≦a≦n and b=0 or 1); and

aryl or heteroaryl having 2 to 30 carbon atoms and their alkyl-, aryl-,heteroaryl-, cycloalkyl-, halogen-, hydroxy-, carboxy-, formyl-, —O—,—CO— or —CO—O-substituted components (e.g. phenyl, 2-methyl-phenyl(2-tolyl), 3-methyl-phenyl (3-tolyl), 4-methyl-phenyl, 2-ethyl-phenyl,3-ethyl-phenyl, 4-ethyl-phenyl, 2,3-dimethyl-phenyl,2,4-dimethyl-phenyl, 2,5-dimethyl-phenyl, 2,6-dimethyl-phenyl,3,4-dimethyl-phenyl, 3,5-dimethyl-phenyl, 4-phenyl-phenyl, 1-naphthyl,2-naphthyl, 1-pyrrolyl, 2-pyrrolyl, 3-pyrrolyl, 2-pyridinyl,3-pyridinyl, 4-pyridinyl or C₆F_((5-a))H_(a) wherein 0≦a≦5),

wherein pairs of the R^(k), R^(m), R^(n), R^(o) may be bonded directlyto each other or via C₁-C₄, which may be substituted if necessary, sothat a saturated, unsaturated, or conjugated unsaturated ring may beformed.

The ionic liquid may have the generic formula [Q⁺]_(a)[A^(a−)], wherein[A^(a−)] with the charge a− is selected out of the group consisting ofthe following molecules in their deprotonated and therefore anionicform:

dialkyl ketones, dialkyl-1,3-diketones, alkyl-β-keto esters, terminalalkines, linear or cyclic 1,3-thioethers, dialkyl phosphonates, dialkylmalonic acid esters, β-cyano carbonic acids and their respectivealkylesters, β-alkoxy carbonic acids and their respective alkylesters,β-cyano nitriles, cyclopentadiene (optionally substituted),trialkylimines, dialkylimines, diaryl ketones, alkyl-aryl-ketones,diaryl-1,3-diketones, alkyl-aryl-1,3-diketones, β-aryloxy carbonic acidsand their respective alkylesters, β-aryloxy carbonic acids and theirrespective arylesters, aryl-β-ketoesters, diarylphosphonates,alkyl-aryl-phosphonates, diaryl malonic acid esters, alkyl-aryl-malonicacid esters, β-cyano carbonic acids arylesters and arylimines.

The ionic liquid may satisfy the generic formula [Q⁺]_(a)[A^(a−)],wherein [A^(a−)] is a carbanion formed by deprotonating a chemicalcompound out of the group consisting of: acetoacetic ester, malonicmononitrile, malonic acid dimethylester, malonic acid diethylester,acetylacetone, malonic acid dinitrile, acetone, diethylketone,methylethylketone, dibutylketone, 1,3-dithian, acetaldehyde,benzaldehyde, crotonaldehyde and butyraldehyde.

The ionic liquid may satisfy the generic formula [Q⁺]_(a)[A^(a−)],wherein [A^(a−)] is a carbanion and wherein [Q]⁺ is one out of the groupconsisting of quaternary ammonium cation [R¹′R¹R²R³N]⁺, phosphonium[R¹′R¹R²R³P]⁺, sulfonium [R¹′R¹R²S]⁺ and a hetero aromatic cation. Thecarbanion may be formed by deprotonating a chemical compound out of thegroup consisting of: acetoacetic ester, malonic mononitrile, malonicacid dimethylester, malonic acid diethylester, acetylacetone, malonicacid dinitrile, acetone, diethylketone, methylethylketone,dibutylketone, 1,3-dithian, acetaldehyde, benzaldehyde, crotonaldehydeand butyraldehyde.

R¹, R¹′, R², and R³ may be alkyl, alkenyl, alkinyl, cycloalkyl,cycloalkenyl, aryl or heteroaryl, which may be independentlysubstituted.

Two of the moieties R¹, R¹′, R², and R³ may form a ring together with ahetero-atom to which they are bound. The ring may be saturated,unsaturated, substituted or unsubstituted. The chain may be interruptedby one or more hetero-atoms out of the group consisting of O, S, NH orN—C1-C₄-alkyl.

The hetero aromatic cation may be a 5 or 6 membered ring comprising atleast one N and if necessary one O and/or one S. The hetero aromaticcation may be substituted or unsubstituted and/or annelated. The heteroaromatic cation may be selected from the group consisting of:

wherein the moieties R may be one of the following: hydrogen,C₁-C₃₀-alkyl, C₃-C₁₂-cycloalkyl, C₂-C₃₀-alkenyl, C₃-C₁₂-cycloalkenyl,C₂-C₃₀-alkinyl, aryl or heteroaryl, wherein the latter seven moietiesmay have one or more halogenic moiety and/or one to three moietiesselected from the group consisting of C₁-C₆-alkyl, aryl, heteroaryl,C₃-C₇-cycloalkyl, halogen, OR^(c), SR^(c), NR^(c)R^(d), COR^(c),COOR^(c), CO—NR^(c)R^(d), wherein R^(c) and R^(d) may be hydrogen,C₁-C₆-alkyl, C₁-C₆-halogenalkyl, cyclopentyl, cyclohexyl, phenyl, tolylor benzyl.

R¹, R¹′, R², and R³ may be hydrogen, alkyl, alkenyl, alkinyl,cycloalkyl, cycloalkenyl, aryl or heteroaryl which may be independentlysubstituted.

Two of the moieties R¹, R¹′, R², and R³ may form a ring together with ahetero-atom to which they are bound. The ring may be saturated,unsaturated, substituted or unsubstituted. The chain may be interruptedby one or more hetero-atoms out of the group consisting of O, S, NH orN—C₁-C₄-alkyl.

R⁴, R⁵, R⁶, R⁷ and R⁸ may be, independently of each other, hydrogen,halogen, nitro, cyano, OR^(c), SR^(c), NR^(c)R^(d), COR^(c), COOR^(c),CO—NR^(c)R^(d), C₁-C₃₀-alkyl, C₃-C₁₂-cycloalkyl, C₂-C₃₀-alkenyl,C₃-C₁₂-cycloalkenyl, aryl or heteroaryl, wherein the latter 6 moietiesmay comprise one or more halogenic moiety and/or one to three moietiesselected out of the group consisting of C₁-C₆-alkyl, aryl, heteroaryl,C₃-C₇-cycloalkyl, halogen, OR^(c), SR^(c), NR^(c)R^(d), COR^(c),COOR^(c), CO—NR^(c)R^(d), wherein R^(c) and R^(d) may be, independentlyof each other, hydrogen, C₁-C₆-alkyl, C₁-C₆-halogenalkyl, cyclopentyl,cyclohexyl, phenyl, tolyl or benzyl.

Two neighboring moieties of the moieties R, R⁴, R⁵, R⁶, R⁷ and R⁸ mayform, together with an atom to which they are bound, a ring which may beunsaturated or aromatic, unsaturated or saturated, wherein the chainformed by the respective moieties may be interrupted by one or morehetero-atoms out of the group consisting of O, S, NH or N—C₁-C₄-alkyl.

R^(e), R^(f), R^(g), and R^(h) may be, independently of each other,hydrogen, C₁-C₆-alkyl, aryl-, heteroaryl-, C₃-C₇-cycloalkyl, halogen,OR^(c), SR^(c), NR^(c)R_(d), COOR^(c), CO—NR^(c)R^(d) or COR^(c),wherein R^(c) and R^(d), may be, independently of each other, hydrogen,C₁-C₆-alkyl, C₁-C₆-halogenalkyl, cyclopentyl, cyclohexyl, phenyl, tolylor benzyl; such as hydrogen, halogen, and C₁-C₆-alkyl, or hydrogen andC₁-C₆-alkyl.

The ionic liquid that may be part of the sorbant fluid or may even formthe main component of the sorbant fluid and may be designed according tospecific needs. In general the ionic liquid may satisfy the genericformula ([A]⁺)_(a)[B]^(a−), wherein [A]⁺ is one out of the groupconsisting of quaternary ammonium cation [R¹′R¹R²R³N]⁺, phosphoniumcation [R¹′R¹R²R³P]⁺, sulfonium cation [R¹′R¹R²S]⁺, a hetero aromaticcation and guanidinium cation R³R³′N(C═NR¹R¹′)NR²R²′, such as:

In case of the quaternary ammonium [R¹′R¹R²R³N]⁺, phosphonium[R¹′R¹R²R³P]⁺ or sulfonium [R¹′R¹R²S]⁺ cation, R¹, R¹′, R², and R³ maybe hydrogen or alkyl, alkenyl, alkinyl, cycloalkyl, cycloalkenyl, arylor heteroaryl which may be independently substituted.

Two of the moieties R¹, R¹′, R², and R³ may form a ring together with ahetero-atom to which they are bound. The ring may be saturated,unsaturated, substituted or unsubstituted. The chain may be interruptedby one or more hetero-atoms out of the group consisting of O, S, NH orN—C₁-C₄-alkyl.

In case of the guanidinium R³R³′N(C═NR¹R¹′)NR²R²′ cation, R¹, R¹′, R²,R²′ R³, R³′ may be hydrogen or alkyl, alkenyl, alkinyl, cycloalkyl,cycloalkenyl, aryl or heteroaryl which may be independently substituted.Two of the moieties R¹, R¹′, R², R³, R³′ may form a ring without ortogether with a hetero-atom to which they are bound. The ring may besaturated, unsaturated, substituted or unsubstituted. The chain may beinterrupted by one or more hetero-atoms out of the group consisting ofO, S, NH or N—C₁-C₄-alkyl.

Two of the moieties R¹, R¹′, R², R³ may form a ring together with ahetero-atom to which they are bound. The ring may be saturated,unsaturated, substituted or unsubstituted. The chain may be interruptedby one or more hetero-atoms out of the group consisting of O, S, NH orN—C₁-C₄-alkyl.

The cation [A]⁺ may be a hetero aromatic cation and may form a five- orsix-membered ring comprising at least one N and if necessary one Oand/or one S. The hetero aromatic cation may be substituted,unsubstituted, and/or annelated. The hetero aromatic cation may beselected from the group consisting of:

wherein the moieties R may be one of the following: hydrogen,C₁-C₃₀-alkyl, C₃-C₁₂-cycloalkyl, C₂-C₃₀-alkenyl, C₃-C₁₂-cycloalkenyl,C₂-C₃₀-alkinyl, aryl or heteroaryl, wherein the latter seven moietiesmay have one or more halogenic moiety and/or one to three moietiesselected from the group consisting of C₁-C₆-alkyl, aryl, heteroaryl,C₃-C₇-cycloalkyl, halogen, OR^(c), SR^(c), NR^(c)R^(d), COR^(c),COOR^(c), CO—NR^(c)R^(d).

R^(c) and R^(d) may be hydrogen, C₁-C₆-alkyl, C₁-C₆-halogenalkyl,cyclopentyl, cyclohexyl, phenyl, tolyl or benzyl.

R¹, R¹′, R², and R³ may be hydrogen, alkyl, alkenyl, alkinyl,cycloalkyl, cycloalkenyl, aryl or heteroaryl which may be independentlysubstituted.

Two of the moieties R¹, R¹′, R², and R³ may form a ring together with ahetero-atom to which they are bound. The ring may be saturated,unsaturated, substituted or unsubstituted. The chain may be interruptedby one or more hetero-atoms out of the group consisting of O, S, NH orN—C₁-C₄-alkyl.

R⁴, R⁵, R⁶, R⁷ and R⁸ may be, independently of each other, hydrogen,halogen, nitro, cyano, OR^(c), SR^(c), NR^(c)R^(d), COR^(c), COOR^(c),CO—NR^(c)R^(d), C₁-C₃₀-alkyl, C₃-C₁₂-cycloalkyl, C₂-C₃₀-alkenyl,C₃-C₁₂-cycloalkenyl, aryl or heteroaryl, wherein the latter six moietiesmay comprise one or more halogenic moiety and/or one to three moietiesselected out of the group consisting of C₁-C₆-alkyl, aryl, heteroaryl,C₃-C₇-cycloalkyl, halogen, OR^(c), SR^(c), NR^(c)R^(d), COR^(c),COOR^(c), CO—NR^(c)R^(d), wherein R^(c) and R^(d) may be, independentlyof each other, hydrogen, C₁-C₆-alkyl, C₁-C₆-halogenalkyl, cyclopentyl,cyclohexyl, phenyl, tolyl or benzyl.

Two neighboring moieties of the moieties R, R⁴, R⁵, R⁶, R⁷ and R⁸ mayform, together with an atom to which they are bound, a ring which may bearomatic, unsaturated or saturated, wherein the chain foiled by therespective moieties may be interrupted by one or more hetero-atoms outof the group consisting of O, S, NH or N—C₁-C₄-alkyl.

R^(e), R^(f), R^(g), and R^(h) may be, independently of each other,hydrogen, C₁-C₆-alkyl, aryl-, heteroaryl-, C₃-C₇-cycloalkyl, halogen,OR^(c), SR^(c), NR^(c)R^(d), COOR^(c), CO—NR^(c)R^(d) or COR^(c),wherein R^(c) and R^(d), may be, independently of each other, hydrogen,C₁-C₆-alkyl, C₁-C₆-halogenalkyl, cyclopentyl, cyclohexyl, phenyl, tolylor benzyl, such as hydrogen, halogen, C₁-C₆-alkyl, or hydrogen andC₁-C₆-alkyl.

[B]^(a−) may be carboxylate of the generic form (Vd) [R^(n)—COO]⁻,wherein R^(n) may be one organic, saturated, unsaturated, acyclic,cyclic, aliphatic, aromatic or araliphatic moiety comprising carbon orhydrogen and having one to thirty (30) carbon atoms, which may compriseone or more heteroatoms and/or which may be substituted by one or morefunctional groups or halogen.

The moiety R^(n) in the above carboxylate may be organic, saturated,unsaturated, acyclic, cyclic, aliphatic, aromatic or araliphaticmoieties comprising carbon and having one to thirty (30) carbon atoms:C₁- to C₃₀-alkyl and the respective aryl-, heteroaryl-, cycloalkyl-,halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO—, —CO—O— or—CO—N substituted components, for example, methyl, ethyl, 1-propyl,2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl(isobutyl),2-methyl-2-propyl(tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl,2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl,2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl,3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl,3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl,3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl,3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl,3,3-dimethyl-2-butyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl,nonadecyl, icosyl, henicosyl, docosyl, tricosyl, tetracosyl, pentacosyl,hexacosyl, heptacosyl, octacosyl, nonacosyl, triacontyl, phenylmethyl(benzyl), diphenylmethyl, triphenylmethyl, 2-phenylethyl,3-phenylpropyl, cyclopentylmethyl, 2-cyclopentylethyl,3-cyclopentylpropyl, cyclohexylmethyl, 2-cyclohexylethyl,3-cyclohexylpropyl, methoxy, ethoxy, formyl, acetyl orC_(n)F_(2(n-a)+(1-b))H_(2a+b) wherein n≦30, 0≦a≦n and b=0 or 1 (e.g.CF₃, C₂F₅, CH₂CH₂—C_((n-2))F_(2(n-2)+1), C₆F₁₃, C₈F₁₇, C₁₀F₂₁, C₁₂F₂₅);C₃- to C₁₂-cycloalkyl and the respective aryl-, heteroaryl-,cycloalkyl-, halogen-, hydroxy-, carboxy-, formyl-, —O—, —CO— orCO—O-substituted components (e.g. cyclopentyl, 2-methyl-1-cyclopentyl,3-methyl-1-cyclopentyl, cyclohexyl, 2-methyl-1-cyclohexyl,3-methyl-1-cyclohexyl, 4-methyl-1-cyclohexyl orC_(n)F_(2(n-a)−(1-b))H_(2a-b) wherein n≦30, 0≦a≦n and b=0 or 1);

C₂- to C₃₀-alkenyl and the respective aryl-, heteroaryl-, cycloalkyl-,halogen-, hydroxyl-, amino-, carboxy-, formyl-, —O—, —CO— or —CO—O—substituted components (e.g. 2-propenyl, 3-butenyl, cis-2-butenyl,trans-2-butenyl or C_(n)F_(2(n-a)−(1-b))H_(2a-b) wherein n≦30, 0≦a≦n andb=0 or 1);

C₃- to C₁₂-cycloalkenyl and the respective aryl-, heteroaryl-,cycloalkyl-, halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO— or—CO—O— substituted components (e.g. 3-cyclopentenyl, 2-cyclohexenyl,3-cyclohexenyl, 2,5-cyclohexadienyl or C_(n)F_(2(n-a)−3(1-b))H_(2a-3b)wherein n≦30, 0≦a≦n and b=0 or 1); and

aryl or heteroaryl having two to thirty (30) carbon atoms and therespective alkyl-, aryl-, heteroaryl-, cycloalkyl-, halogen-, hydroxy-,amino-, carboxy-, formyl-, —O—, —CO— or —CO—O— substituted components(e.g. phenyl, 2-methyl-phenyl (2-tolyl), 3-methyl-phenyl (3-tolyl),4-methyl-phenyl, 2-ethyl-phenyl, 3-ethyl-phenyl, 4-ethyl-phenyl,2,3-dimethyl-phenyl, 2,4-dimethyl-phenyl, 2,5-dimethyl-phenyl,2,6-dimethyl-phenyl, 3,4-dimethyl-phenyl, 3,5-dimethyl-phenyl,4-phenyl-phenyl, 1-naphthyl, 2-naphthyl, 1-pyrrolyl, 2-pyrrolyl,3-pyrrolyl, 2-pyridinyl, 3-pyridinyl, 4-pyridinyl or C₆F_((5-a))H_(a),wherein 0≦a≦5) hydrogen, methyl, trifluoromethyl, pentafluoroethyl,phenyl, carboxy-phenyl(protonated or deprotonated),hydroxyphenyl-methyl, trichloromethyl, dichloromethyl, chloromethyl,trifluoromethyl, difluoromethyl, fluoromethyl, unbranched or branchedC₁- to C₁₂-alkyl, unbranched or branched C₁- to C₁₂-mono-, di-, tri- orpolyhydroxy-alkyl, unbranched or branched C₁- to C₁₂-mono-, di-, tri- orpolycarboxy-alkyl (with fully deprotonated, partially deprotonated orfully protonated carboxy groups), unbranched or branched C₁- toC₁₂-mono-, di-, tri- or polycarboxy-hydroxyalkyl (with fullydeprotonated, partially deprotonated or fully protonated carboxygroups), unbranched or branched C₁- to C₁₂-mono-, di-, tri- orpolycarboxy-dihydroxy-alkyl (with fully deprotonated, partiallydeprotonated or fully protonated carboxy groups), unbranched or branchedC₁- to C₁₂-mono-, di-, tri- or polycarboxy-trihydroxy-alkyl (with fullydeprotonated, partially deprotonated or fully protonated carboxygroups), unbranched or branched C₁- to C₁₂-mono-, di-, tri- orpolycarboxy-polyhydroxy-alkyl (with fully deprotonated, partiallydeprotonated or fully protonated carboxy groups), unbranched or branchedC₁- to C₁₂-alkenyl, unbranched or branched C₁- to C₁₂-mono-, di-, tri-or polyhydroxy-alkenyl, unbranched or branched C₁- to C₁₂-mono-, di-,tri- or polycarboxy-alkenyl (with fully deprotonated, partiallydeprotonated or fully protonated carboxy groups), unbranched or branchedC₁- to C₁₂-mono-, di-, tri- or polycarboxy-hydroxyalkenyl (with fullydeprotonated, partially deprotonated or fully protonated carboxygroups), unbranched or branched C₁- to C₁₂-mono-, di-, tri- orpolycarboxy-dihydroxy-alkenyl (with fully deprotonated, partiallydeprotonated or fully protonated carboxy groups), unbranched or branchedC₁- to C₁₂-mono-, di-, tri- or polycarboxy-trihydroxy-alkenyl (withfully deprotonated, partially deprotonated or fully protonated carboxygroups), unbranched or branched C₁- to C₁₂-mono-, di-, tri- orpolycarboxy-polyhydroxy-alkenyl (with fully deprotonated, partiallydeprotonated or fully protonated carboxy groups). R^(n) may be methyl,ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl,2-methyl-1-propyl(isobutyl), 2-methyl-2-propyl(tert-butyl), 1-pentyl,2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl,2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl,2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl,4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl,4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl,2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 2-ethyl-1-butyl,2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, heptyl, octyl, nonyl, decyl,undecyl or dodecyl). Carboxylate (Vd) may be trichloroacetate,dichloroacetate, chloroacetate, trifluoroacetate, difluoroacetate,fluoroacetate, methoxyacetate, cyanacetate, glykolate, benzoate,pyruvate, malonate, pivalate and the deprotonated or partiallydeprotonated form of the following monovalent or polyvalent acids:formic acid; acetic acid; propionic acid; butyric acid; valeric acid;caproic acid; enanthic acid; caprylic acid; capric acid; lauric acid;myristic acid; palmitic acid; stearic acid; arachidic acid;O-acetylsalicylic acid; sorbic acid; pivalic acid; fatty acids; aminoacids (e.g. isoleucine, alanine, leucine, asparagine, lysine, asparticacid, methionine, cysteine, phenylalanine, glutamic acid, threonine,glutamine, tryptophan, glycine, valine, proline, serine, tyrosine,arginine, histidine, ornithine, taurine, sulfamic acid); sugar acids(linear or cyclic form) (e.g. aldonic acids, (HOOC—(CHOH)_(n)—CH₂OH, n=1to 4); ulosonic acids; uronic acids; aldaric acids (HOOC—(CHOH)n—COOH,n=1 to 4); gluconic acid; glucuronic acid; mannonic acid; mannuronicacid; galactonic acid; galacturonic acid; ascorbic acid; glyceric acid;xylonic acid; neuraminic acid; iduronic acid; dicarboxylic acids (e.g.oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid,isophthalic acid, terephthalic acid, maleic acid, fumaric acid,glutaconic acid, traumatic acid, muconic acid); tricarboxylic acids(e.g. citric acid, isocitric acid, aconitic acid,propane-1,2,3-tricarboxylic acid, trimesic acid); hydroxy-carboxylicacids (e.g. glycolic acid, lactic acid, malic acid, citric acid,tartaric acid, mandelic acid, 2-hydroxybutyric acid, 3-hydroxybutyricacid, 4-hydroxybutyric acid, 3-hydroxypropionic acid,3-hydroxyisovaleric acid, salicylic acid); and polycarboxylic acids.

The anion may be written in the form [RCO₂ ⁻], wherein [RCO₂ ⁻] is oneout of the group consisting of carboxylate, formiate, acetate,propionate, butyrate, benzoate, and salicylate.

The anion can be written in the form [RCO₂ ⁻], wherein [RCO₂ ⁻] is acarboxylate and wherein R is a radical out of the group consisting ofC₁-C₃₀-alkyl, C₃-C₁₂-cycloalkyl, C₂-C₃₀-alkenyl, C₃-C₁₂-cycloalkenyl,C₂-C₃₀-alkinyl, aryl and heteroaryl. The moiety or radical R maycomprise or include one or more halogen radicals.

The anion can be written in the form [RCO₂ ⁻], wherein [RCO₂ ⁻] is acarboxylate wherein R represents one to three radicals out of the groupconsisting of C₁-C₆-alkyl, aryl, heteroaryl, C₃-C₇-cycloalkyl, halogen,cyanide, OR^(c), SR^(c), NR^(c)R^(d), COR^(c), COOR^(c), CO—NR^(c)R^(d),wherein R^(c) and/or R^(d), is one of the group consisting of hydrogen,C₁-C₆-alkyl, C₁-C₆-halogenalkyl, cyclopentyl, cyclohexyl, phenyl, tolyl,and benzyl.

The anion can be written in the form [RCO₃ ⁻], wherein [RCO₃ ⁻] is acarbonate wherein R represents one to three radicals out of the groupconsisting of, hydrogen, C₁-C₆-alkyl, aryl, heteroaryl,C₃-C₇-cycloalkyl, halogen, cyanide, OR^(c), SR^(c), NR^(c)R^(d),COR^(c), COOR^(c), CO—NR^(c)R^(d), wherein R^(c) and/or R^(d), is one ofthe group consisting of hydrogen, C₁-C₆-alkyl, C₁-C₆-halogenalkyl,cyclopentyl, cyclohexyl, phenyl, tolyl, and benzyl. Alternatively, theanion may be carbonate, i.e. CO₃ ²⁻.

The anion may be choline carbonate. By sorbing CO₂ the choline carbonate(CAS 59612-50-9) may form choline hydrogencarbonate (CAS 78-73-9). Thecholine hydrogencarbonate may be regenerated to choline carbonate againby heating the same.

The anion may be selected from acetate, carbonate, dichloroacetate,chloroacetate, difluoroacetate, fluoroacetate, methoxyacetate,cyanacetate, glykolate, benzoate, pyruvate, malonate, pivalate, thedeprotonated or partially deprotonated form of the following monovalentor polyvalent acids: formic acid, acetic acid, propionic acid, butyricacid, valeric acid, caproic acid, enanthic acid, caprylic acid, capricacid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidicacid, O-acetylsalicylic acid, sorbic acid, pivalic acid, fatty acids,isoleucine, alanine, leucine, asparagine, lysine, aspartic acid,methionine, cysteine, phenylalanine, glutamic acid, threonine,glutamine, tryptophan, glycine, valine, proline, serine, tyrosine,arginine, histidine, ornithine, taurine, sulfamic acid, aldonic acids,ulosonic acids, uronic acids, aldaric acids, gluconic acid, glucuronicacid, mannonic acid, mannuronic acid, galactonic acid, galacturonicacid, ascorbic acid, glyceric acid, xylonic acid, neuraminic acid,iduronic acid, oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaricacid, glutaconic acid, traumatic acid, muconic acid, citric acid,isocitric acid, aconitic acid, propane-1,2,3-tricarboxylic acid,trimesic acid, glycolic acid, lactic acid, malic acid, citric acid,tartaric acid, mandelic acid, 2-hydroxybutyric acid, 3-hydroxybutyricacid, 4-hydroxybutyric acid, 3-hydroxypropionic acid,3-hydroxyisovaleric acid, salicylic acid, polycarboxylic acids, andmixtures thereof.

Cations may be selected out of the group consisting of: mono-, di-,tri-, or tetra-alkyl-ammonium, mono-, di-, tri-, ortetra-alkylphosphonium, trialkylbenzylammonium, with one to fourindependent C₁ to C₆-alkyl chains; 1,3-dialkylimidazolium,1,2,3-trialkylimidazolium, N-alkylpyridinium, N,N-dialkylpiperidinium,N,N-dialkylmorpholinium, N,N-dialkylpyrrolidinium with one or twoindependent C₁ to C₆-alkyl chains; and mono-, di-, tri-, tetra-, penta-or hexa-alkylguanidinium, with one to six independent C₁ to C₆-alkylchains, which may be substituted with one or more hydroxy- oralkoxy-groups, or 2-Hydroxyethyltrimethylammonium (Choline),2-Acetoxyethyl-trimethylammonium (Acetylcholine) or Guanidinium(protonated Guanidine, CAS 113-00-8).

The cation may be a quaternary or protonated cation chosen from thegroup consisting of ammonium, phosphonium, sulfonium, piperidinium,pyrrolidinium and morpholinium.

The cation may be one chosen from the group consisting oftrialkylmethylammonium, tetramethylammonium, triethylmethylammonium,tributylmethylammonium, trioctylmethylammonium, trialkylammonium,trimethylammonium, triethylammonium, tributylammonium, andtrioctylammonium. The trialkylmethylammonium may be aC₁-C₁₀-trialkylmethylammonium.

The cation may be one chosen from the group consisting oftetramethylammonium, triethylmethylammonium, tributylmethylammonium, andtrioctylmethylammonium.

A method using an ionic liquid to sorb vapors having an electricmulti-pole moment is provided. The vapor may be CO₂ or H₂O, while theionic liquid may be an organic salt having a melting temperature ofbelow 200° C., below 100° C., or preferably below 20° C. such as organicsalts that may be quaternary salts having a generic formula of:([A]⁺)_(a)[B]^(a−) The described method may be useful for processes inwhich CO₂ or H₂O are to be removed as pure substance or a gas or vapormixture independent of whether CO₂ or H₂O is a main or secondarycomponent or a working medium. Applications may include using an ionicliquid as a desiccant in a dehumidifier or air conditioning unit basedon ionic liquid/H₂O or ionic liquid/CO₂ as working media, or removingCO₂ or H₂O out of, for example, ambient air.

Cations of the above ionic liquids may be selected fromtetramethylammonium, tetraethylammonium, tetrabutylammoniumtetrahexylammonium, tetraoctylammonium, trimethylammonium,triethylammonium, tributylammonium, triethylmethylammonium,tributylmethylammonium, trihexylmethylammonium, trioctylmethylammonium,tris-(2-Hydroxyethyl)methylammonium, tris-(2-Hydroxyethyl)ethylammonium,bis-(2-hydroxyethyl)dimethylammonium, 1,3-dimethylimidazolium,1-ethyl-3-methylimidazolium, 1-propyl-3-methylimidazolium,1-butyl-3-methylimidazolium, 1,2,3-trimethylimidazolium,1,3-diethylimidazolium, 1,3-dibutylimidazolium,1-ethyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium,1-(2-hydroxyethyl)-3-methylimidazolium,1-(3-hydroxypropyl)-3-methylimidazolium,1-(2-hydroxypropyl)-3-methylimidazolium,1-(4-hydroxy-butyl)-3-methylimidazolium,1-(3-hydroxy-butyl)-3-methylimidazolium,1-(2-hydroxy-butyl)-3-methylimidazolium,1-(2-methoxyethyl)-3-methylimidazolium,1-(3-methoxypropyl)-3-methylimidazolium,1-(2-methoxypropyl)-3-methylimidazolium,1-(4-methoxy-butyl)-3-methylimidazolium,1-(3-methoxy-butyl)-3-methylimidazolium,1-(2-methoxy-butyl)-3-methylimidazolium,1-(2-ethoxyethyl)-3-methylimidazolium,1-(3-ethoxypropyl)-3-methylimidazolium,1-(2-ethoxypropyl)-3-methylimidazolium,1-(4-ethoxy-butyl)-3-methylimidazolium,1-(3-ethoxy-butyl)-3-methylimidazolium,1-(2-ethoxy-butyl)-3-methylimidazolium, 1-allyl-3-methylimidazolium,1-allyl-2,3-dimethylimidazolium, N,N-dimethylmorpholinium,N,N-diethylmorpholinium, N,N-dibutylmorpholinium,N-ethyl-N-methylmorpholinium, N-butyl-N-methylmorpholinium,N,N-dimethylpiperidinium, N,N-diethylpiperidinium,N,N-dibutylpiperidinium, N-ethyl-N-methylpiperidinium,N-butyl-N-methylpiperidinium, N,N-dimethylpyrrolidinium,N,N-diethylpyrrolidinium, N,N-dibutylpyrrolidinium,N-ethyl-N-methylpyrrolidinium, N-butyl-N-methylpyrrolidinium,2-Hydroxyethyltrimethylammonium (choline),2-acetoxyethyl-trimethylammonium (acetylcholine), guanidinium(protonated guanidine, CAS 113-00-8), tetramethylguanidinium,pentamethylguanidinium, hexamethylguanidinium triethylmethylphosphonium,tripropylmethylphosphonium, tributylmethylphosphonium,tetraethylphosphonium, tetrapropylphosphonium, tetrabutylphosphonium,tetramethylphosphonium, and mixtures thereof.

CO₂ Removal Cycle

The cycle may be able to provide a high level of removal of CO₂ from thegas stream and also a high concentration of CO₂ in the concentratedstream when the material has a higher equilibrium pickup of CO₂ atconditions in the adsorber than it has in the desorber. In embodiments,the sorbent material may hold more CO₂ at ambient temperature and thedesired final CO₂ concentration, than it does at the desorptiontemperature and in a 100% CO₂ atmosphere.

In FIG. 6 an isotherm of EMMIM acetate is shown in varying levels ofCO₂, up to 1%, and less than 1% relative humidity. It clearly shows thateven at a 1% CO2 concentration in the gas the sorbent will hold over 3%of its weight in CO₂.

In FIG. 7 the isotherm for the same material in a 100% CO₂ atmosphere athigher temperatures is shown. It can be seen that that material gives upnearly all of its CO₂ at temperatures at nearly 100° C. in a pure CO₂environment. Thus, the possibility of rendering the CO₂ level below 1%or lower seems practical if regeneration takes place at temperaturesabove 90° C. in pure or less than pure CO₂ environments.

Allowing the ionic liquid adsorbent to flow counter to the flow of thedried stack gas stream may optimize the system. Thus, the mostconcentrated adsorbent contacts the most cleansed gas stream, and as thesorbent picks up CO₂ it contacts a gas stream with increasing CO₂concentration enabling further adsorption of CO₂ until a maximum amountis collected. Once again, as low a flow of sorbent material as possibleshould be utilized so as to maximize the concentration of CO₂ in thediluted sorbent. However, by reducing the flow to low levels, such asless that 50 kg sorbent per kg CO₂ transferred. The heat of condensationmay play a role and the gas stream will increase in temperature as theCO₂ stream is removed. Thus, a separate cooling means may be used in theabsorber to remove this heat and allow the sorbent to sorb the CO₂ at aslow a temperature as is possible without detrimental energy costs.

In embodiments, such as the one shown in FIG. 8, the absorber tower 800may include cooling structures 850-853. The number of cooling structuresis not limited and will vary according to the dimensions of the absorbertower and the cooling requirements. The structures function to cool boththe flow of liquid sorbent, as well as the flow of CO₂ laden gas. Thecooling structures may be cooled by any means, such as, for example,cooling tower water or other liquid or gas coolants. The coolingstructures keep the gas stream temperature close to the local ambientwet bulb temperature. For example, a gas stream 810 from the moistureremoval system may enter at the bottom of the absorber tower and thesorbent 840 may be sprayed by a sprayer into the absorber tower. Thecooling structure may have variable temperatures (i.e., the temperatureof cooling structure 850 may be different than the temperature ofcooling structure 851 an so on). However, final cooling to a lower levelcan be employed towards the end of the contact region between the gasand the sorbent, around cooling structure 850, so as to further enhancethe removal of the CO₂ from the gas stream. This allows a CO₂ reducedgas stream 830 to exit the absorber tower, while CO₂ rich sorbent iscollected in a liquid state at the bottom of the absorber tower 800,where it may be transferred to the desorber.

Examples of these types of cooling surfaces are illustrated byLowenstein, for example in U.S. Pat. Nos. 5,351,497; 6,745,826; and7,269,966. However, simpler methods, such as employing more standardcooling coils throughout the contact zone between the sorbent and thegas stream may also be used.

Referring to FIG. 9, the thus diluted CO₂ laden sorbent may then betransferred to the desorber tower 900 or plurality of towers. To reduceheat requirements, the sorbent 910 may first enter a heat exchanger 950with the concentrated sorbent 940 returning from the desorber tower 900.In the desorber tower, the sorbent is flowed over heated surfaces930-934, where it warms and liberates the CO₂ to the surroundingCO₂-rich environment. The number of heated surfaces is not limited andwill vary depending on the size of the desorber tower and the heatingrequirements. The CO₂ gas 920 may then be removed by a pump andpressurized to the desired level for transport and use. The pump mayalso reduce the pressure in the one or more of the desorber towers 900to below ambient pressure so as to further remove CO₂ from the sorbentor to enable regeneration at lower temperatures. Thus, the decision onthe final pressure of the regenerator is one of energy optimization(i.e., the cost of higher grade heat to increase the sorbent to a highertemperature) to more fully regenerate the sorbent and the resulting lossof power from the plant, versus the added electrical or energy cost topower the compressor or pump with a higher differential pressure. Theheating of the sorbent may also be staged, wherein the sorbent ispreheated to a lower temperature using lower grade heat, or is heated ina first vessel on surfaces at a lower temperature before beingtransferred to a next vessel with higher temperature surfaces forfurther enrichment, etc. In this manner the amount of high-grade heatutilized can be minimized. For example, the heated surfaces in thedesorber tower near the entrance of the CO₂-rich stream may be heated bylow-grade heat, such as from the coolant stream from the moistureremoval system, and the heated surfaces near the CO₂ free sorbent may beheated by high-grade heat.

Solid Sorbent

In embodiments using solid sorbent, such as that shown in FIG. 10, forthe CO₂ capture and removal, a multiple tower system 1000 may be used.The CO₂ laden gas 1020 from the above moisture removal system isdirected, such as by a two-way valve 1010, to the bottom of a tower 1030containing sorbent. As the CO₂ laden gas passes through the sorbent1040, the sorbent sorbs the CO₂ and allows a CO₂ free gas 1080 to exitthe top of the tower. Once the sorbent in the tower becomes saturatedwith CO₂, the CO₂ laden gas is directed by the two-way valve 1010 to adifferent tower 1050 that is packed with a solid sorbent, and thesorbent in the first tower is regenerated.

The sorbent may be regenerated by heating the tower, such as byintroducing hot air into the tower or by other external or internalheating means. The application of heat to the saturated sorbent allowsthe CO₂ that was sorbed to the sorbent to be released in a gaseousstate. The gaseous CO₂ may then be removed through a CO₂ bleed line 1070as isolated CO₂ that may be further processed for storage or use.

Solid sorbents for use in the solid sorbent CO₂ removal system may beselected from molecular sieve materials, such as 4A, 5A or 13X, zeoliteX, zeolite Y, silica, mordenite or activated carbon. The solid sorbentmay also be a metal oxide. Suitable metal oxides may include alkaliearth metal oxides, transition metal oxides, alkaline earth metal oxide,such as CaO and MgO.

Finally, it should be noted that the above-mentioned embodimentsillustrate rather than limit the invention, and that those skilled inthe art will be capable of designing many alternative embodimentswithout departing from the scope of the invention as defined by theappended claims. In the claims, any reference signs placed inparentheses shall not be construed as limiting the claims. The word“comprising” and “comprises,” and the like, does not exclude thepresence of elements or steps other than those listed in any claim orthe specification as a whole. The singular reference of an element doesnot exclude the plural reference of such elements and vice-versa. In adevice claim enumerating several means, several of these means may beembodied by one and the same item of software or hardware. The mere factthat certain measures are recited in mutually different dependent claimsdoes not indicate that a combination of these measures cannot be used toadvantage.

What is claimed is:
 1. A moisture removal apparatus comprising: amoisture transfer device; a cooling device; an enthalpy exchange device;and a CO₂ removal system, wherein a gas stream is received by adesorption portion of the moisture transfer device, the gas stream iscooled by the cooling device after being received by the desorptionportion of the moisture transfer device, the enthalpy of the gas streamis decreased by an enthalpy decreasing portion of the enthalpy exchangedevice after the gas stream is cooled by the cooling device, the gasstream is received by an adsorption portion of the moisture transferdevice after the enthalpy of the gas stream is decreased by the enthalpyexchange device, and the gas stream is sent to the CO₂ removal systemafter being received by the adsorption portion of the moisture transferdevice.
 2. The apparatus according to claim 1, wherein the gas streamfrom the CO₂ removal system is sent to an enthalpy increasing portion ofthe enthalpy exchange device.
 3. The apparatus according to claim 1,wherein a temperature of the gas stream that enters the desorptionportion of the moisture transfer device is 90° C. or greater.
 4. Theapparatus according to claim 1, wherein an absolute humidity of the gasstream that enters the desorption portion of the moisture transferdevice is greater than 40 g/kg.
 5. The apparatus according to claim 3,wherein the dew point temperature of the gas stream entering the CO₂removal system is at least 20° C. below the dew point of the gas streamthat enters the desorption portion of the moisture transfer device. 6.The apparatus according to claim 5, wherein the absolute humidity of thegas stream entering the CO₂ removal system is less than 4 g/kg.
 7. Theapparatus according to claim 6, wherein the absolute humidity of the gasstream entering the CO₂ removal system is less than 1 g/kg.
 8. Theapparatus according to claim 1, wherein the moisture transfer devicecomprises a solid or liquid desiccant.
 9. The apparatus according toclaim 8, wherein the moisture transfer device comprises an ionic liquiddesiccant.